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Re: [TLS] SHA-3 in SignatureScheme

Eric Rescorla <ekr@rtfm.com> Fri, 02 September 2016 11:34 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 02 Sep 2016 04:32:06 -0700
Message-ID: <CABcZeBM-4=ostcAkDhM=jk1aRtXD4dXZKz_ymjShFWmStH3otQ@mail.gmail.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] SHA-3 in SignatureScheme
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On Fri, Sep 2, 2016 at 3:42 AM, Ilari Liusvaara <ilariliusvaara@welho.com>
wrote:

> On Fri, Sep 02, 2016 at 12:08:47PM +0200, Hubert Kario wrote:
> > On Thursday, 1 September 2016 19:22:18 CEST Dave Garrett wrote:
> > >
> > > The reason I see is that we currently specify exactly one valid hash
> > > algorithm (in a variety of sizes). The precedent argument is good
> enough
> > > for me. I think adding it in this document is definitely worth
> considering.
> > > I don't want to wait until SHA-2 is considered weak to provide an
> > > alternative, if we can avoid it.
> >
> > I've created a PR for it: https://github.com/tlswg/tls13-spec/pull/616
> >
> > I haven't changed any recommendations, the recommended hashes to
> implement are
> > still SHA-2 based, and I don't think we should change that given that
> > certificates just now are transitioning to SHA-256 because of
> incompatibility
> > fears.
>
> Just tweaking the signatures is not enough. There is also the PRF hash,
> and using weak hash there has, umm... rather bad consequences.
>
> I also don't see why this should be in TLS 1.3 spec, instead of being
> its own spec (I looked up how much process BS it would be to get the
> needed registrations: informative RFC would do).
>

I also am not following why we need to do this now. The reason we defined
SHA-2 in
a new RFC was because (a) SHA-1 was looking weak and (b) we had to make
significant
changes to TLS to allow the use of SHA-2. This does not seem to be that
case.

-Ekr


>
> -Ilari
>
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